Kyra Harper

Sarah repels a potentially lethal Topside menace as she fights to locate a disappeared Helena, and the threat of Castor looms anew.

Leda and Castor are both on the hunt for original clone DNA, while a shocking revelation about their connection leaves the sisters reeling.

Castor pursues the Leda clones for original tissue samples; Helena, who's pregnant and imprisoned, is examined by a mysterious new villain.

Helena and her sister are reunited at the Castor camp when Sarah is captured. As Sarah suffers testing, Paul appears to hide her.

Mark is taken down in a Prolethean shoot-out and Sarah must step in to help. Alison and Donnie come face-to-face with Jason Kellerman.

Paul finds the truth behind the Castor Boys' logbooks of names, pushing him into action; Felix is desperate for info on Sarah's whereabouts.